The present invention relates to a lower electrode structure used in applying plasma processing, such as etching, to a substrate such as a semiconductor substrate. The present invention also relates to a plasma processing apparatus using the lower electrode structure.
In a manufacturing process for a semiconductor device etc., processing within a high vacuum, such as a plasma etching, is frequently employed. However, when processing is performed under the high vacuum, vacuum adsorption cannot be used for holding a substrate such as a semiconductor substrate (hereinafter referred to as xe2x80x9cwaferxe2x80x9d) since the vacuum adsorption is usually applicable in the air. For this reason, the wafer is usually held by a mechanical means such as a clamp.
When the wafer is held by the clamp, the distal end of the clamp comes into contact with an edge or a working surface of the wafer. As a result, dust is generated at the time the clamp comes into contact with the wafer and sometimes contaminates the wafer surface.
To overcome these problems, a holding means called an electrostatic chuck has been widely used.
FIG. 4 is a schematic view of a lower electrode structure having the electrostatic chuck.
A lower electrode structure 100 shown in FIG. 4 has a susceptor 101 formed of aluminium and an electrostatic chuck 102 formed thereon.
The electrostatic chuck 102 has a dielectric layer 103 having a mounting surface for mounting a wafer W thereon and a flat electrode 104 arranged in the dielectric layer 103. The susceptor 101 is connected to a high frequency source 106 via a matching box 105. On the other hand, to a flat electrode 104, a direct-current source 108 is connected by way of a low pass filter 107.
In the lower electrode structure 100 having the aforementioned structure, when a high frequency power is supplied from the high frequency source 106 to the susceptor 101; at the same time a direct-current voltage is applied from the direct-current source 108 to the flat electrode 104, electrostatic attraction such as a Coulomb force is produced between the flat electrode 104 and the wafer W mounted on the dielectric layer 103. As a result, the dielectric layer 103 attracts the wafer W and holds it.
When such a lower electrode structure 100 is arranged in a chamber of a plasma processing apparatus such as a plasma etching apparatus, and the chamber is vacuumed, and then, a high frequency power is supplied from the high frequency source 106 to the susceptor 101, a high frequency electric field is formed in the vicinity of a working surface of the wafer W.
Thereafter, when a process gas is introduced into the chamber, a plasma of the process gas is produced due to the high frequency electric field. The plasma is applied to the wafer W to perform plasma etching.
However, if the frequency of the high-frequency power to be supplied from the high frequency source 106 to the susceptor 101 is, for example, 2 MHz or less, the dielectric layer 103 interposed between the wafer W and the susceptor 101 prevents the high frequency from passing through. As a result, the high frequency electric field is rarely converged on the wafer W, decreasing etching characteristics. In particular, when the dielectric layer 103 is formed of ceramic, this tendency is significantly observed.
Different from the lower electrode structure shown in FIG. 4 another type of lower electrode structure shown in FIG. 5 is known.
A lower electrode structure 110 differs from that shown in FIG. 4. A high frequency power 106 is connected to a flat electrode 104 via a matching box 105 and a capacitor 11. The direct-current voltage from the direct-current source 108 is superimposed on the high frequency voltage supplied from the high frequency source 106 and then applied to the flat electrode 104.
According to the lower electrode structure 110 mentioned above, a dielectric layer 103 can pass a high frequency through it, compared with the lower electrode structure 100 shown in FIG. 4, whereby the high frequency electric field can be easily converged on the wafer W.
In the meantime, the heat conductivity under the high vacuum is lower than that under normal pressure, due to the extremely low amount of heat-conductive medium. In the plasma processing performed under the high vacuum, a helium gas pipe 112 for supplying helium gas for heat transmission to a space between the wafer W and the dielectric layer 103 is arranged, as shown in FIG. 5. Due to this, the temperature of the wafer W can be controlled even under the high vacuum.
However, the lower electrode structure shown in FIG. 5 has a problem in that an abnormal discharge occurs within the helium gas pipe 112 when helium gas is supplied.
An object of the present invention is to provide a lower electrode structure capable of forming a high frequency electric field which capable of applying satisfactory plasma processing on a substrate without an abnormal discharge and to provide a plasma processing apparatus using the lower electrode structure.
To attain the aforementioned object, the present invention provides a lower electrode structure for use in an apparatus for applying plasma processing to a substrate, comprising:
a base table formed of a material having a conductivity;
an electrostatic adsorption member formed on the base table and having a dielectric layer on which the substrate to be mounted and within which an electrode electrically isolated from the base table is housed;
first wiring having an end connected to the electrode of the electrostatic adsorption member
a direct-current source connected to the other end of the first wiring;
second wiring having an end connected to the base table;
a high frequency source connected to the other end of the second wiring;
a third wiring for connecting the first wiring and the second wiring; and
a first capacitor formed on the third wiring.
The present invention provides a plasma processing apparatus comprising:
a chamber for applying plasma processing to a substrate while holding airtight;
a lower electrode structure housed in the chamber and having a mounting surface for the substrate;
an upper electrode arranged in the chamber so as to face the mounting surface of the lower electrode structure;
an exhaust system for exhausting the chamber;
a process gas supply system for introducing a process gas into the chamber;
the lower electrode structure comprising
a base table formed of a conductive material
a dielectric layer formed on the base table and having a mounting surface for the substrate;
an electrostatic adsorption member formed within the dielectric layer and having an electrode electrically isolated from the base table;
first wiring having an end connected to the electrode of the electrostatic adsorption member;
a direct-current source connected to the other end of the first wiring;
second wiring having an end connected to the base table;
a high frequency source connected to the other end of the second wiring;
a third wiring for connecting the first wiring and the second wiring; and
a first capacitor formed on the third wiring,
wherein a plasma of the process gas is formed in the chamber by a high frequency power output from the high frequency source and applied to the substrate, thereby performing a predetermined plasma processing.
In the present invention, the high frequency source is connected to the base table by way of the second wiring and a high frequency voltage is applied to the base table; on the other hand, the high frequency source is connected to the first wiring which connects the electrode of the electrostatic adsorption member to the direct-current source, by way of the third wiring having a capacitor. Therefore, the high frequency voltage is superimposed on the direct-current voltage to be applied to the electrode of the electrostatic adsorption member. Since the high frequency voltage is applied not only to the base table but also the electrode of the electrostatic adsorption member as described, the high frequency can be effectively passed without being interrupted by the electrostatic adsorption member. As a result, the high frequency electric field can be converged on the substrate, thereby performing satisfactory plasma processing.
Furthermore, a high frequency voltage is applied by the third wiring to both of the electrostatic adsorption member and the base table. However, due to the presence of a capacitor in the third wiring, a direct-current voltage is not superimposed on the second wiring. Since the phase difference of the high frequency voltages to be applied to the electrode of the electrostatic adsorption member and the base table can be reduced to a minimum, an abnormal discharge within the substrate can be prevented.
The abnormal discharge presumably occurs in the lower electrode structure when the potential difference between members adjacent to each other exceeds a predetermined value. When a direct-current voltage is applied to the electrode of the electrostatic adsorption member and a high frequency voltage is applied to the base table, an extremely large potential difference is periodically produced between the electrode and the base table. As a result, an abnormal discharge occurs.
Under the circumstance, if the potential difference between the electrode of the electrostatic adsorption member and the base table is constantly set within a predetermined narrow range as described above, the abnormal discharge can be prevented even if a pipe for supplying a heat transmission gas such as helium gas, is formed within the base table.
It is preferable that the present invention further comprise a capacitor which is formed on the second wiring and interposed between the base table and a connecting point between the second wiring and the third wiring.
Since the capacitor is interposed, it is possible to control the phases of the high frequency powers to be applied to the electrode of the electrostatic adsorption member and the base table. If the phase difference is reduced to a minimum, the abnormal discharge can be prevented.
In this case, if the phase of the high frequency to be applied to the electrode of the electrostatic adsorption member is allowed to coincide with that to be applied to the base table, the abnormal discharge can be most efficiently prevented.
To describe more specifically, if the capacitor to be arranged to the second wiring has the same capacitance as that of the capacitor to be applied to the third wiring, the impedance from the connecting point between the second wiring and the third wiring to the flat electrode can be made equal to that from the connecting point to the base table. As a result, the phase of the high frequency to be applied to the electrode of the electrostatic adsorption member is allowed to coincide with that to be applied to the base table.